A dental prosthesis often comprises a crown or bridge restoration in which a dental porcelain is fused to a supporting metal or ceramic substrate. Dental porcelains are generally a mixture of glass frit components or natural feldspars or the like. There are a number of key considerations in selecting frit components to form a porcelain that will be compatible with the selected substrate.
For example, the porcelain must have a coefficient of thermal expansion that is as close as possible to that of the substrate. Otherwise, a porcelain fused to the substrate will tend to crack and separate from its supporting structure.
Another key factor in selecting a porcelain component is its effect upon processing temperature of the porcelain; that is, the temperature that must be utilized in fusing the porcelain to the substrate. Fusing temperatures of porcelain materials of the prior art have generally been on the order of 900.degree. C. or higher. Such elevated temperatures limit the composition of the substrate that may be used since some alloys or ceramic compositions will distort or otherwise suffer detrimental compositional changes under such processing conditions.
In selecting glass components and their amounts in the porcelain composition to achieve low-fusing temperatures and appropriate coefficients of thermal expansion, care also must be exercised to insure that the changes in composition do not otherwise adversely effect the qualities of the resulting fired porcelain with respect to its performance in a dental environment. Such characteristics of concern are acid resistance, hardness, flexural strength and the like.
Thus, heretofore, it has remained the goal of researchers to produce a porcelain glass frit composition that has a low-fusing or processing temperature and a coefficient of thermal expansion such that it can be used in combination with both metal and porcelain substrates in dental prostheses. Such a composition would have improved versatility for use in making, repairing or improving crowns, bridges, linings for dentures or as finish porcelains and stains.